LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: "Tobin C. Harding" <me@tobin.cc>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Theodore Ts'o <tytso@mit.edu>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Randy Dunlap <rdunlap@infradead.org>,
	Kees Cook <keescook@chromium.org>,
	Anna-Maria Gleixner <anna-maria@linutronix.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Arnd Bergmann <arnd@arndb.de>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 3/3] vsprintf: Use hw RNG for ptr_key
Date: Wed, 16 May 2018 07:09:55 +1000	[thread overview]
Message-ID: <20180515210955.GF10152@eros> (raw)
In-Reply-To: <20180515094744.45267e97@gandalf.local.home>

On Tue, May 15, 2018 at 09:47:44AM -0400, Steven Rostedt wrote:
> On Tue, 15 May 2018 13:06:26 +1000
> "Tobin C. Harding" <me@tobin.cc> wrote:
> 
> > Currently we must wait for enough entropy to become available before
> > hashed pointers can be printed.  We can remove this wait by using the
> > hw RNG if available.
> > 
> > Use hw RNG to get keying material.
> > 
> > Suggested-by: Kees Cook <keescook@chromium.org>
> > Signed-off-by: Tobin C. Harding <me@tobin.cc>
> > ---
> >  lib/vsprintf.c | 19 ++++++++++++++++---
> >  1 file changed, 16 insertions(+), 3 deletions(-)
> > 
> > diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> > index b82f0c6c2aec..3697a19c2b25 100644
> > --- a/lib/vsprintf.c
> > +++ b/lib/vsprintf.c
> > @@ -1657,9 +1657,8 @@ char *device_node_string(char *buf, char *end, struct device_node *dn,
> >  static bool have_filled_random_ptr_key __read_mostly;
> >  static siphash_key_t ptr_key __read_mostly;
> >  
> > -static void fill_random_ptr_key(struct random_ready_callback *unused)
> > +static void ptr_key_ready(void)
> >  {
> > -	get_random_bytes(&ptr_key, sizeof(ptr_key));
> >  	/*
> >  	 * have_filled_random_ptr_key==true is dependent on get_random_bytes().
> >  	 * ptr_to_id() needs to see have_filled_random_ptr_key==true
> 
> Nothing to do with this patch, but I believe there's a missing memory
> barrier in the code.
> 
> Right after this we have:
> 
> 	smp_mb();
> 	WRITE_ONCE(have_filled_random_ptr_key, true);
> 
> Where the comment says that have_filled_random_ptr_key must be set
> after ptr_key has been updated. But there's no memory barrier on the
> read side. In fact, I think this could be a smp_wmb() instead of a
> smp_mb(). The read side has:
> 
> 	if (unlikely(!have_filled_random_ptr_key))
> 		return string(buf, end, "(ptrval)", spec);
> 
> /* Missing memory barrier smp_rmb() here. */
> 
> 	hashval = (unsigned long)siphash_1u64((u64)ptr, &ptr_key);
> 
> Thus we can have something like:
> 
> 	CPU0				CPU1
> 	----				----
> 				   load ptr_key = 0
>    store ptr_key = random
>    smp_mb()
>    store have_filled_random_ptr_key
> 
> 				   load have_filled_random_ptr_key = true
> 
> 				    BAD BAD BAD!
> 
> I'll send a patch.

Awesome reviewing.  Thanks for catching this.


	Tobin

      reply	other threads:[~2018-05-15 21:09 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-15  3:06 [PATCH v4 0/3] enable early printing of hashed pointers Tobin C. Harding
2018-05-15  3:06 ` [PATCH v4 1/3] random: Fix whitespace pre random-bytes work Tobin C. Harding
2018-05-15  3:06 ` [PATCH v4 2/3] random: Return nbytes filled from hw RNG Tobin C. Harding
2018-05-15 13:37   ` Steven Rostedt
2018-05-15 21:17     ` Tobin C. Harding
2018-05-15 21:35       ` Steven Rostedt
2018-05-15 22:26         ` Tobin C. Harding
2018-05-15  3:06 ` [PATCH v4 3/3] vsprintf: Use hw RNG for ptr_key Tobin C. Harding
2018-05-15 13:47   ` Steven Rostedt
2018-05-15 21:09     ` Tobin C. Harding [this message]

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20180515210955.GF10152@eros \
    --to=me@tobin.cc \
    --cc=akpm@linux-foundation.org \
    --cc=anna-maria@linutronix.de \
    --cc=arnd@arndb.de \
    --cc=gregkh@linuxfoundation.org \
    --cc=keescook@chromium.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=rdunlap@infradead.org \
    --cc=rostedt@goodmis.org \
    --cc=torvalds@linux-foundation.org \
    --cc=tytso@mit.edu \
    --subject='Re: [PATCH v4 3/3] vsprintf: Use hw RNG for ptr_key' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).